Dot matrix impact line printers have been designed over the years to provide for dots in a matrix configuration to form alphabetical and numerical symbols. Such printers can generally be described as having hammersprings with a tip. The tip at the end of each hammerspring is formed oftentimes from a tungsten carbide rod. The tungsten carbide rod is extremely hard and durable.
Such dot matrix printers can be exemplified by the patents assigned to the assignee of this invention, namely Printronix, Inc. An example of such technology can be seen in U.S. Pat. No. 3,941,051.
In these types of printers, the hammersprings historically have been formed of a uniform spring such as a leaf spring. At the end of the leaf spring, a tip or rod is fitted and brazed into an opening of the spring. Before brazing, the tungsten carbide rod is pressed into the steel base of the spring and then brazed to the spring steel.
The reliability of a brazing process in combination with a pressed fit although extremely functional over the years has been obviated by this invention. This specific invention utilizes a resistance welding process of the tungsten carbide to the steel in a superior manner by resistance welding.
The method of welding when combined with the hammersprings of this invention and the tungsten carbide tips becomes a unique process for today's printers to provide high speed, high durability and substantial reliability which is not known in the art.
Further to this invention, is a hammerspring that is configured to provide for extremely effective impact by utilizing the full capability of the mass of the spring and its spring potential.
The respective process for welding the tungsten carbide rod to the steel base of the spring steel of the hammerspring is accomplished by utilization of the cobalt in the tungsten carbide. The cobalt in the tungsten carbide flows in a manner to provide for a weld which is superior to that in the prior art. It particularly flows so as to create a weld and maximizes the connection through an enhanced and broadened base fillet or gusset to the weldment.
The parameters of the welding process include an appropriate electrode design, a welding program, as well as a certain amount of mechanical force by the electrode, and the respective cooling in adjacent relationship to the electrode.
The tungsten carbide rod or tip can be of any suitable size and shape. The steel of the spring can be any low carbon steel or low alloy steel. The net result is to achieve a significant bonding between the tungsten carbide rod or tip and the hammersprings of this invention for improved operation.
An enhanced feature of this invention is the hammerspring configuration in conjunction with the welded rod or tip. This particular hammerspring configuration in conjunction with the welded rod allows for significantly higher operating speeds as well as long life and durability. As a consequence, it is believed that the method and apparatus as provided by the teachings of this invention are a significant step over the prior art.